Stable and Active AuCu and AuPd Electrocatalysts for Platinum-Free Oxygen Reduction Reaction: Design Principles from Ligand–Strain Coupling and Gold Surface Segregation

Abstract

Surface–subsurface partitioning of alloying elements affects stability, strain, and adsorption energetics in heterogeneous catalysis yet remains difficult to control. Here, we use first-principles calculations and atomistic modeling to show that AuM binary alloys (M = Cu, Pd) provide a model platform for understanding this coupling at the atomic scale. We investigate AuxsurfM100–xsurf surface alloys supported on fcc(111) substrates AuxsubM100–xsub, spanning pure metals, monolayers, mixed alloys, and segregated surface–subsurface configurations. We find that alloy stability is governed by a coupled mechanism in which Au segregates to the surface, lowers the surface energy, and generates a self-compressive surface strain that tunes the adsorption of reaction intermediates. A surface that is compressive on average exhibits a lower likelihood of strong intermediate binding and enhanced catalytic activity, particularly in monolayer alloys. However, an average compressive strain does not imply uniform local compression across the surface. Instead, we construct strain maps that show that tensile and compressive regions coexist across the alloyed surfaces. As a result, averaged strain fails to capture adsorption energetics across bridge, atop, and hollow sites. Using the oxygen reduction reaction (ORR) as a model electrocatalytic system, we reveal that reliable adsorption energetics emerge from a site-specific net ligand–strain coupling shaped by both short- and long-range effects. Ordered surface alloys, notably the Au33Cu67/Cu(111) and the dilute Au14Pd86/Pd(111) single-atom alloy, are predicted to be promising, combining near-optimal ORR adsorption energetics with greater structural stability than the corresponding pure-metal surfaces. These results establish a framework linking Au segregation, surface stability, and catalytic response in strain-engineered alloy catalysts.